This invention relates to electrolysis apparatus and to electrode structure in such apparatus.
As a result of recent shortages in hydrocarbon fuels and the recognition that the supply of such fuels will ulimately be exhausted, there has naturally been an increased interest in finding and developing alternative fuels. Hydrogen, being one of the most abundant of all elements and being relatively pollution free when burned, is considered one of the more attractive alternatives to hydrocarbon fuels, and electrolysis is considered one of the more attractive and economically feasible methods of producing hydrogen.
Prior art electrolytic cells have typically included a container of some type for holding a liquid electrolyte and a pair of electrodes immersed in the electrolyte. Application of direct current across the electrodes produces an electrochemical reaction in which the electrolyte is decomposed into one or more gas products. For example, with an aqueous electrolyte, oxygen and hydrogen may be produced.
Because of the inefficiencies, portability drawbacks, and unreliability of the liquid electrolyte cells, considerable interest has centered on a fairly new technology involving solid polymer electrolytes (SPE). See, for example, "Solid Electrolytes Offer Route to Hydrogen", Chemical and Engineering News, Aug. 27, 1973; "Electrolytic Hydrogen Fuel Production with Solid Polymer Electrolyte Technology" by W. A. Titterinton and A. P. Fickett, VIII IECEC Proceedings; and "A Hydrogen-Energy System", published by American Gas Association, 1973. As described in these references, SPE is typically a solid plastic sheet of perfluorinated sulfonic acid polymer which, when saturated with water, becomes an excellent ionic conductor. The ionic conductivity results from the mobility of the hydrogen ions which move through the polymer sheet by passing from one sulfonic acid group to another. An anode and cathode are positioned on either side of the sheet and pressed thereagainst to form the desired SPE cell.
Hydrogen is produced by the SPE cell by supplying water to the anode where it is electrochemically decomposed to provide oxygen, hydrogen ions, and electrons. The hydrogen ions move through the SPE sheet to the cathode while the electrons pass through the external circuit. At the cathode, the hydrogen ions and the electrons recombine electrochemically to produce hydrogen gas.
Although the prior art SPE cell described provides a reliability and efficiency not achieved with the liquid electrolyte cell, the cell still requires noble metal catalysts and thus is quite costly. In addition, cell breakdown is more frequent than is desirable.